1. Field of the Invention
The invention relates to the use of an admixture of compounds as an anti-sludge agent in an acid environment and, more particularly, to the use of a combination of dicyclopentadiene and a naturally occurring mixture of cyclic monoterpenes isolated from Pinus species to reduce the formation of sludge arising from acid stimulation of oil-containing formations which are subject to sludge formation.
2. Prior Art
Various acids are used to stimulate subterranean hydrocarbon-bearing formations. The acid functions to dissolve acid soluble materials in the formation so as to increase the permeability of the formation. The permeability increase is effected by cleaning or enlarging flow channels leading to the well bore allowing more oil or gas to flow to the well bore.
Formation of sludges by certain crude oils on contact with various acids has been recognized as a serious problem in areas of California and Canada for some time. Following acidizing treatments, the wells are very slow to clean up, if at all, and often a large quantity of asphalt-like material is returned with the treatment fluid. Interaction studies between sludging crude oils and acids have shown that precipitated solids or films are formed at the acid oil interface. The precipitates are mainly asphaltenes, resins, paraffins and other high-molecular weight hydrocarbons. No films are observed for non-sludging crudes with acids.
Once the sludges are formed they are often difficult to remove or control. It has been suggested that the best solution to the sludging problem is to prevent sludge formation. An explanation of why and how sludges are formed and some methods of sludge prevention are described in the article entitled "Formation, Effect and Prevention of Asphaltene Sludges During Stimulation Treatments" by E. W. Moore et al, Journal of Petroleum Technology, September 1965, pp. 1023-1028.
Methods for preventing or reducing sludge formation include the addition of alkyl phenols, fatty acids, surfactants and the like to stabilize the acid-oil emulsion against sludge formation. The various materials suffer from various problems during use. The anti-sludge agents may be incompatible with other additives such as corrosion inhibitors used in the acid, suffer from poor dispersibility in acids or brines, or be corrosive to metals and the like.
It is an object of this invention to attempt to overcome at least some of the problems experienced by the currently known anti-sludging agents.